Questions and Answers About Integrated Fixed-Film/Activated Sludge (IFAS) in a BNR Pilot Plant

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Integrated Fixed-film/Activated Sludge (IFAS) is an increasingly popular technology that promises to greatly improve the performance of activated sludge wastewater treatment systems.  However, many questions remain about the fundamental behaviors and performance of these hybrid systems. Their future development will require a better understanding of the biokinetic behaviors and distribution of specific organisms in the IFAS biofilms, including the effects of media placement, on these parameters. For this reason a team of researchers from Duke University, Entex Technologies Inc, Ashbrook Simon-Hartley, CH2M Hill and Hazen and Sawyer are conducting an in-depth pilot study of IFAS at the South Durham Water Reclamation Facility in North Carolina. This paper provides early data from this study, providing key insights to how such systems should be designed and the expected benefits.

INTRODUCTION
Integrated fixed film activated sludge (IFAS) systems are hybrid biological wastewater treatment systems consisting of microbial activity in both suspended phase, as in conventional activated sludge systems, and a fixed (biofilm) phase. The fixed phase is included through the addition of solid media, often to conventional activated sludge reactors, which provides a surface for biofilm growth. The media used is typically some form of extruded, honey-comb like plastic media (e.g. BioPortzTM, Entex Technologies), or a series of mesh netting screens through which the waste stream flows (BioWebTM, Entex Technologies). The addition of IFAS media greatly increases microbial mass in biological reactors, which accelerates the removal rates of soluble contaminants and provides additional capacity relative to conventional systems in the same volume. A major motivation for the use of these systems is to cost-effectively increase plant capacity, particularly with respect to nitrification, which is thought to be encouraged because the IFAS media provides a relatively stable environment with a long solids retention time (SRT) for slow growing, nitrifying bacteria.

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